In areas with severe winters such as North America and Russia, studded tires are primarily used as winter tires. Conventionally, in a studded tire, a plurality of implanting holes for embedding stud pins are provided in a tread portion, and stud pins are embedded in these implanting holes. Implanting holes are ordinarily formed into a cylindrical shape. On the other hand, there are single flange type stud pins having a flange portion on the bottom side of a cylindrical body portion so that the flange portion bulges to a greater degree than the body portion, and double flange type stud pins having flange portions on the road contact surface side and the bottom side of a cylindrical body portion so that the flange portions bulge to a greater degree than the body portion, but double flange type stud pins have become mainstream in recent years (for example, see Japanese Unexamined Patent Application Publication No. 2010-70052A). The performance of a studded tire is exhibited by the stud pins embedded in the tread portion, but when the stud pins fall off, the reduction in performance on snow and ice is marked, so a countermeasure against pin dropping has become an important issue.
In recent years, increases in safety awareness in the market have led to greater demands for performance on snow and ice and wet performance in studded tires. Therefore, there is a demand to suppress the falling off of stud pins—that is, to improve the stud pin retention capacity beyond conventional levels.